Impact modifier combination for aromatic polyesters

ABSTRACT

An improved toughened blend of an aromatic polyester with from 5 to 20 phr of an impact modifier, which impact modifier is a blend of (a) 80 to 85 weight percent of a core/shell impact modifier having a polybutadiene core and at least one shell formed from methyl methacrylate and styrene; and (b) 15 to 20 weight percent of a linear copolymer which contains from 50 to 85 parts of units derived from ethylene, from 5 to 40 parts of units derived from (meth)acrylic esters, and from 2 to 10 parts of a copolymerizable monomer containing an epoxy group. The toughened blend exhibits higher impact strength than would be calculated for the blend using a linear relationship based on values of notched Izod for two blends, each containing only one of the impact modifiers at an equal use level.

EXAMPLE 1

This Example illustrates the unexpected results for a blend of two impact modifiers in poly(butylene terephthalate). The core/shell impact modifier is a core/shell polymer, prepared essentially as in U.S. Pat. No. 3,985,704, of 77.5 parts of a butadiene/styrene 95/5 core, 11.25 parts of a styrene first stage, and 11.25 parts of a methyl methacrylate second stage. The polymer is stabilized with a mixture of hindered phenols and tris(nonylphenyl)phosphite prior to spray-drying, and has been pelletized prior to blending. The linear terpolymer is believed to be a terpolymer containing about 70% of ethylene, 25 to 30% of ethyl acrylate and 2 to 8% glycidyl methacrylate. Blends are made with poly(butylene terephthalate) of each modifier separately at 18%, and of a combination of modifiers (15 parts core/shell and 3 parts linear terpolymer).

                                      TABLE I     __________________________________________________________________________                           Linear                   Core/shell                           Terpolymer                                   Calculated                   Impact Modifier                           Impact Modifier                                   for B1            Blend (B1)                   (IM1)   (IM2)   Blend     __________________________________________________________________________     Amount 15 IM1 and 3                   18      18      (adjusted average)            IM2     Izod, -20° C.            647    101     260     128     Izod, -10° C.            795    396     954     489     Izod, +23° C.            851    744     1162    814     __________________________________________________________________________

EXAMPLE 2

This Example illustrates the unexpected results for a blend of two impact modifiers in poly(butylene terephthalate). The core/shell impact modifier is a core/shell polymer, prepared essentially as in U.S. Pat. No. 3,808,180, of 80 parts of a butyl acrylate/trimethylolpropane triacrylate/diallyl maleate terpolymer core, and 20 parts of a methyl methacrylate second stage, of particle size ca. 350 nm., isolated from emulsion by spray-drying. The linear terpolymer is believed to be a terpolymer containing about 70% of ethylene, 25 to 30% of ethyl acrylate and 2 to 8% glycidyl methacrylate. Blends are made with poly(butylene terephthalate) of each modifier separately at 18%, and of a combination of modifiers (15 parts core/shell and 3 parts linear terpolymer).

                                      TABLE II     __________________________________________________________________________                           Linear                   Core/shell                           Terpolymer                                   Calculated                   Impact Modifier                           Impact Modifier                                   for B2            Blend (B2)                   (IM3)-Acrylic                           (IM2)   Blend     __________________________________________________________________________     Amount 15 IM3 and 3                   18      18      (adjusted average)            IM2     Izod, -20° C.            120    84      260     113     Izod, 0° C.            622    136     1058    289     Izod, +23° C.            791    559     1162    659     __________________________________________________________________________

EXAMPLE 3

This Example illustrates the rheology behavior for blends of the two impact modifiers of Example 1 and of Example 2 in poly(butylene terephthalate). Here the conditions are established to obtain a filled mold temperature of a blend of two impact modifiers in poly(butylene terephthalate). The core/shell impact modifier and the linear terpolymer are those of Example I. Binary blends are made at 22% of each modifier, the Vicat softening temperature determined, and the value for 18% calculated by interpolating between these values and the value of unmodified PBT from the literature. The values for the binary blends are then averaged in a 15:3 ratio to estimate the Vicat value for the ternary blend of Example 1 as it would be expected from the values for its components.

The ternary blend of Example I is directly measured; its value of 138° C. is above the value calculated for the blend (134° C.).

                                      TABLE III     __________________________________________________________________________                            Linear                    Core/shell                            Terpolymer                                    Calculated                    Impact Modifier                            Impact Modifier                                    for B3             Blend (B3)                    (IM1)   (IM2)   Blend     __________________________________________________________________________     Composition             15 IM1 and 3                    22; 18 (calc.)                            22; 18 (calc.)                                    (adjusted average)             IM2     Vicat Softening             138    127 (136)                            113 (125)                                    134     Temperature, °C.     18 part value calculated from linear interpolation of 0 and 22 part     values                         taken from 18 part                                    values and linearly                                    averaged     __________________________________________________________________________

EXAMPLE 4

This Example illustrates the rheology behavior for blends, of the two impact modifiers of Example 1 and of Example 2 in poly(butylene terephthalate). Here the conditions are established to obtain a filled mold with good appearance from the unmodified poly(butylene terephthalate), and the melt pressure is measured in bars (1 bar=10⁶ cm.²). Then the various combinations are molded and the pressure developed is recorded. A higher melt pressure is indicative of more difficult molding, generally requiring a higher molding temperature to correct.

                                      TABLE IV     __________________________________________________________________________                             Linear                     Core/shell                             Terpolymer     Core/shell                     Impact Modifier                             Impact Modifier                                            Impact Modifier              Blend (B1)                     (IM1)   (IM2)   Blend (B2)                                            (IM3)     __________________________________________________________________________     Amount   15 IM1 and 3                     18      18      15 IM3 and 3                                            18              IM2                    IM2     Melt pressure, bars*              18     9       33      12     10     __________________________________________________________________________      *Extruder melt pressure reading for adequate molding 

We claim:
 1. A toughened blend consisting essentially of an aromatic polyester with from 5 to 20 parts, per 100 parts of polyester, of an impact modifier, which impact modifier is a blend of(a) 80 to 85 weight percent of a core/shell impact modifier having(1) from 70 to 90 parts of a core of a rubber which is a homopolymer of butyl acrylate or 2-ethylhexyl acrylate or a copolymer of butyl acrylate and/or 2-ethylhexyl acrylate with up to about 30% of at least one other copolymerized vinyl monomer; (2) at least one shell, which one shell is a homopolymer of methyl methacrylate or a copolymer which contains a majority of units derived from either methyl methacrylate or styrene; and (b) 15 to 20 weight percent of a linear copolymer which contains from 50 to 85 parts of units derived from ethylene, from 5 to 40 parts of units derived from a C₁ -C₈ ester of (meth)acrylic acid, and from 2 to 10 parts of a copolymerizable monomer containing an epoxy group,wherein the blend contains essentially no polycarbonate, and wherein the toughened blend exhibits higher impact strength, as measured by a notched Izod test, and a lower melt pressure to achieve acceptable molding, than would be calculated for the blend using a linear relationship based on values of notched Izod or for melt pressure to achieve adequate molding for two blends, each containing only one of the impact modifiers at an equal use level.
 2. The composition of claim 1 wherein the polyester is poly(butylene terephthalate).
 3. The composition of claim 1 wherein the rubber or at least one shell further contains units derived from a multi-unsaturated monomer.
 4. The composition of claim 1 wherein the C₁ -C₈ ester of (meth)acrylic acid of the linear copolymer is ethyl acrylate.
 5. The composition of claim 1 wherein the copolymerizable monomer containing an epoxy group of the linear copolymer is glycidyl methacrylate. 